Arrangement for mounting two coaxial shaftlines

ABSTRACT

In an assembly with two concentric shafts, one of which projects beyond the other, a seal support sleeve placed between them has a conical shape and bears on a spacer of the external shaft, so that an assembly nut of the forward end is accessible to be unscrewed from the back through the space between the two shafts, thus enabling the external shaft to be disassembled. The invention may be applicable to front bearings of gas turbine high pressure shafts and makes it possible to disassemble the high pressure body from behind, without needing to disassemble equipment, such as a fan on the front of the machine, or hindering the installation of a gear.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an assembly for the installation of two coaxial shafts, particularly a so-called low pressure shaft as shown in FIG. 1 connecting the low pressure compressor 1 to the low pressure turbine 2 in a gas turbine, surrounded by a high pressure shaft connecting the high pressure compressor 3 to the high pressure turbine 4.

2. Description of Related Art

In this type of machine, the internal shaft 15 (low pressure) projects beyond the front of the external shaft 16 (high pressure) and can finish at a shaft end 5 supporting a large volume fan 6 on which large radius blades are fitted to discharge air into an auxiliary stream 7 surrounding the main gas stream 8, and if there is an accidental breakage in this fan, there will be a severe out-of-balance mass on the internal shaft 15. Thus, some arrangements need to be made. Firstly, a bearing 9 called the number 1 bearing right at the front of the internal shaft 15 may be made fusible or breakable, in other words it may be installed on a low resistance support 10 that breaks as soon as an out-of-balance mass develops, so that the resulting large forces that are then generated are not transmitted to the rest of the stator structure. The shaft end 5 is then free to tilt by moving under the effect of the out-of-balance mass until the assembly that it forms with the fan 6 moves into a new position in equilibrium in rotation and without necessarily causing any further damage until the machine stops. The shaft end 5 makes this movement tilting around a so-called bearing number 2 behind the previous bearing, that supports its back end and a main shaft in the internal shaft 15. This bearing is denoted reference 17. It thus controls the axial position of the internal shaft 15.

A movement control gear 20, designed particularly to start the machine and activated by a transmission shaft 25 perpendicular to the shafts 15 and 16, must be placed between this bearing 17 and a so-called bearing number 3 (reference 18) that provides support to the forward end of the external shaft 16. The previous shaft bearing 17, being as far backwards as possible to improve the dynamic resistance of the internal shaft 15, is only separated from it by just sufficient space to contain the gear 20. An assembly nut is screwed around the forward end of the external shaft 16 to hold it in place against this bearing 18 by stopping in contact on the bearing. This nut, that extends forwards from the bearing 18 and on the movement control gear 20, is difficult to access, particularly because a seal support sleeve must be placed behind the bearing 17 immediately in front of the nut, overlapping the forward end of the external shaft 16 and a portion of the internal shaft 15 to create a seal between them. Disassembly of the high pressure shaft 16, before maintenance, is usually only possible after disassembling the machine in front of the nut, and particularly the fan 6, so that it can be reached and unscrewed.

Refer to French patent 2 783 579 for a description of an assembly by which the nut can be unscrewed from behind using a special tool inserted into the annular space between the shafts, which is more convenient despite the fact that this space is narrow since there is then no need for any major disassembly of elements of the machine to be able to remove the high pressure shaft; but the selected assembly consists of screwing the nut in the external shaft whereas it is conventionally screwed around the shaft, which changes the entire design of the forward end of the shaft and it can introduce other disadvantages. In this case, another solution is proposed to provide easy access to the nut holding the external shaft 16 in place from behind without making any major change to the design; the narrow space around the nut makes a few modifications to surrounding parts of the machine necessary, but it will be seen that they are mainly applicable to sealing and movement control devices, for which the design is less restrictive.

BRIEF SUMMARY OF THE INVENTION

In its most general form, the representative assembly of the invention comprises coaxial internal and external shafts, a forward part of the internal shaft projecting beyond a forward end of the external shaft, a sleeve surrounding the shafts and supporting a seal associated with each of the shafts, a bearing supporting the external shaft close to the forward end and a bearing retaining nut screwed around the forward end, characterized in that it comprises a spacer with an adjustment part slid around the external shaft and tightened between the nut and the bearing, and a sealing part arranged around the nut and on which the seal associated with the external shaft rubs.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of this arrangement and other aspects of the invention will be discovered after reading the commentary on the following figures:

FIG. 1, already described, is an overview of a gas turbine;

FIG. 2 shows an_assembly prior to the invention and in which the problems of access to the nut mentioned above were not solved;

FIG. 3 shows an assembly conform with the invention; and

FIG. 4 shows a view of another assembly conform with the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows a portion of the internal shaft 15, the forward end of the external shaft 16, one end of the number 2 bearing 17, the number 3 bearing 18, the assembly nut 19 of bearing 18, the movement control gear 20, a crown wheel 21 engaged with the gear 20 and retained between the external shaft 16, the nut 19 and the bearing 18 to participate in the assembly of the bearing 18 as a thrust bearing, the seal support sleeve 22, its two seals 23 and 24 rubbing on contiguous portions of shafts 15 and 16; and the environment of the gear 20 comprises a transmission shaft 25 connected in rotation to the gear 20 by splines 26 and engaged in a hub 27 of the gear 20; a pair of bearings 28 and 29 engaged around the hub 27; a housing 30 connected by screwing to an extension 31 of the sleeve 22 and (at right in the figure) to a casing 32 of the stator; and a shell 33 screwed to the housing 30 that retains the bearing 29 on the far end from gear 20, while the other bearing 28 close to the gear 20 is driven by the hub 27 and slides in the housing 30; collars 34 and 35 of the bearing 28 close to the gear 20 and the shell 33 are applied in thrust on the housing 30 and are screwed to it to keep the bearings 28 and 29 in a fixed position along the hub 27. The attachment screws are not shown to simplify the drawing. The means of retaining the bearings 28 and 29 include nuts, thrust washers, force fitted sleeves, in a known manner. In this case, the bearing 28 is a ball bearing and the other bearing 29 is a roller bearing, without an internal ring and in which the rollers bear directly on the hub 27.

It is worthwhile mentioning the method of fitting the assembly onto the gear 20 after the nut 19 has been screwed into place. The gear 20, the bearing 28 adjacent to it and the housing 30 are installed by screwing the housing onto the casing 32, and the shell 33 and the bearing 29 are then installed by fixing the shell to the housing 30, and the seal support sleeve 22 is fixed to the housing 30 by sliding it backwards; finally the transmission shaft 25 is inserted in the hub 27. It is seen that the nut 19, well surrounded by other parts, has become inaccessible unless major disassembly operations are carried out. Since the seal 24 rubs on a lip 14 of the external shaft 16 that extends forwards from the nut 19 and the nut is screwed around this shaft 16, the seal support sleeve 22 completely separates the nut 19 from the annular space 13 between the shafts 15 and 16.

FIG. 3 illustrates a first embodiment of the invention and firstly shows a modification to the seal support sleeve, which in this case is assigned reference 38 and which has a conical shape, the seal 39 on the side of the high pressure shaft 16 now having a larger diameter than the unchanged seal 23 on the side of the low pressure shaft 15; the seal 39 does not rub on the actual shaft 16, but rather on a sealing contact surface 41 of a spacer 40 integrated into the high pressure shaft 16 and being provided for this purpose with a thrust contact surface 42 inserted on the said shaft and compressed by the nut 19 between it and the crown wheel 21.

The result of this is that the sealing contact surface 41 and the sleeve 38 surround the nut 19 instead of covering it at the front and thus it becomes accessible from behind, using a tool with claws not shown that can be slid in the annular space 43 between the shafts 15 and 16, and in that the nut 19 is at the forward end of the shaft 16, the lip 14 that it surrounded having been replaced by the sealing contact surface 41. The reference 44 is assigned to a locking part of the nut 19 that comprises crab teeth penetrating into the nut 19 and the external shaft 16 to prevent any relative rotation when it is put into place; it is in the form of a split ring and is made of an elastic material so that it can be opened to put it into place.

Some arrangements may be proposed at the side of the gear 20 to adapt the structure to modify the shape of the seal support sleeve 38; there are the two bearings 28 and 29 of the hub support 27 of the gear 20, the housing 30 fixed to the extension 31 of the seal support sleeve 38 and the casing 32, but in this case the shell 33 is replaced by a different shell 45 that extends around the two bearings 28 and 29, and still supports the thrust collar 35 forming the attachment to the housing 30.

The assembly is different from the assembly in FIG. 2. It is made by fixing the housing 30, and then consists of inserting the gear 20 fitted with the bearing closest to it (in this case 29) into the housing 30, placing it on a thrust surface 50 at the bottom of the housing 30, sliding the seal support sleeve 38 above the gear 20 and fixing it to the housing 30. The shell 45 fitted with the bearing on the remote side of the gear 20 (in this case the ball bearing 28) is then inserted into the reaming in the housing 30 and around the hub 27 and the bearing 29. The bearing 28 supports a spacer ring 51 that finally touches the other bearing 29 during this movement, pushes it back and thus lifts the gear 20. When the collar 35 stops in contact with the housing 30, the gear 20 engages with the crown wheel 21. The transmission shaft 25 is finally installed.

FIG. 4 represents a variant of this idea in which bearings 28 and 29 occupy the same positions as in the previous design and in which the shell 33 is also used; but the thrust collar 34 of the bearing 28 placed on the edge of the housing 30 is replaced by a collar 46 placed under it, and the collar 35 of the shell 33 with which it is in contact. The assembly is made approximately in the same way as before, except that the bearings 28 and 29 must both be put into place after the gear 20 has been put into place in the housing 30.

The innovation of the assembly according to the invention can be explained as follows. The only way to access the nut 19 from the front, which was the only possible way before, is to slide the seal support sleeve 22 forwards, separating it from the housing 30. This movement to lift the seal support sleeve in the forward direction is no longer useful with the invention, and it is even impossible since the flared rear part of the seal support sleeve 38 would stop in contact with the teeth of the gear 20. Thus, it would also be a problem to assemble the housing 30 if the seal support sleeve 38 were moved forwards, since its raised front edge would be stopped in contact with the flared rear part of the housing. Therefore, an assembly was adopted in which the seal support sleeve 38 is pulled clear backwards during assembly of the housing 30 and the gear 20; its attachment flange 47 stops in contact with the housing 30 at the back, unlike the situation in the previous assembly. The assembly does not cause any difficulty provided that the gear 20 can be lowered to the bottom of the housing 30 so that it does not collide with the attachment flange 47 or other parts of the seal support sleeve 38 before it is in its final position, which is perfectly possible if the bearing 28, which is a ball bearing designed to support the gear 20 in the vertical direction (or the radial direction in the gas turbine) is fixed to the housing 30 later after having been inserted below the housing, then lifting the gear 20.

The assembly in FIG. 3 with a single shell 45 for the vertical support bearing 28 of the gear 20 and the other bearing 29, installed free to slide in the vertical direction, is simpler and probably more rigid, but it makes it necessary to change over the conventional positions of the bearings, and assembly can be more complicated due to the larger size of the shell 45. This is why the more ordinary assembly in FIG. 4, in which the main difference in the method of assembly of bearings 28 and 29 is the position of the collar 46, has many merits. 

1. An assembly comprising: an internal shaft and an external shaft, said internal and external shafts being coaxial and a forward part of the internal shaft projecting beyond a forward end of the external shaft; a sleeve surrounding the shafts and holding first and second seals, the first seal sealing a portion of the internal shaft and the second seal sealing a portion of the external shaft; a first bearing supporting the forward end of the external shaft; a nut screwed around said forward end for providing a stop for said first bearing; and a spacer having a first part adjusted around the external shaft and retained between the nut and the first bearing, and a second part extending around the nut on which the second seal sealing with the external shaft rubs.
 2. (canceled)
 3. The assembly according to claim 1, further comprising: a gear arranged under the nut, the spacer and the sleeve in a direction substantially perpendicular to both shafts; a gear support housing surrounding the gear; and a gear hub holding the gear in said direction, wherein a second bearing for the gear is installed around a shaft of the gear by an ascending displacement from below the housing, and the sleeve comprises a flange in abutment with a part of the housing, the abutment being obtained by a forward displacement of the flange.
 4. The assembly according to claim 3, further comprising: a single shell fixed to the housing, in which the second bearing and a third bearing installed around the shaft of the gear are installed.
 5. The assembly according to claim 1, wherein a diameter of the second seal is larger than a diameter of the first seal.
 6. The assembly according to claim 1, wherein the sleeve is conical. 